1. Field of the Invention
The present invention relates to a driving device for a liquid crystal display panel and a liquid crystal display device having the driving device and more particularly to the driving device for a liquid crystal display panel and the liquid crystal display device capable of performing an overshooting driving operation in which an overvoltage exceeding a target voltage to be reached at time of completion of a response of a liquid crystal is applied to increase a response speed of the liquid crystal.
The present application claims priority of Japanese Patent Application No. 2006-077254 filed on Mar. 20, 2006, which is hereby incorporated by reference.
2. Description of the Related Art
A conventional liquid crystal display device is so configured that displaying of a gray shade is achieved by changing a voltage to be applied to a liquid crystal layer making up a liquid crystal display panel for every pixel in each frame to change transmittance of a liquid crystal. Moreover, in order to obtain a desired gray-level value (target gray level) by a rapid response of a liquid crystal even when a comparatively abrupt change in gray levels (that is, a change in transmittance) is requested, an overshooting operation is performed in which a specified overvoltage exceeding a target voltage corresponding to a target gray level to be reached at time of completion of a response is applied [(for example, see Patent Reference 1 (Japanese Patent Application Laid-open No. 2002-2295219)].
The conventional liquid crystal display device 101, as shown in FIG. 14, has a liquid crystal display panel 102 and a driving circuit 103 to drive the liquid crystal display panel 102. The driving circuit 103 includes an overshoot calculating section 104 to calculate a proper overshoot amount, a storing section 105 to store processing programs, various blocks of data, or a like, a timing control section 106 to control output timing of video signals, a data electrode driving circuit 107 to supply displaying signals (data signals) to each signal line of the liquid crystal display panel 102, and a scanning electrode driving circuit 108 to supply scanning signals to each scanning line. The liquid crystal display device 101 is, for example, a normally white mode liquid crystal display panel.
The storing section 105 has a frame memory 109 serving as an image memory and an LUT (hereinafter, Look Up Table) storing section 110 to store the LUT. The frame memory 109 stores one frame of image data. The LUT storing section 110 stores the LUT containing gray-level data for overshooting driving corresponding to transition of gray levels In the LUT, an overshoot amount corresponding to transition of gray levels (combination of a gray level in one past frame and a gray level in a current frame for displaying) is shown as an increase of a gray-level value relative to a target gray-level value.
The overshoot calculating section 104 detects an overshoot amount corresponding to a gray-level value of an input current frame (n-th frame video data Fn) and a gray-level value of one past frame [(n−1)-th frame video data Fn−1] obtained from the frame memory 109 from an LUT stored in the LUT storing section 110 and outputs gray-level data obtained by addition of the overshoot amount thereto so that a corresponding voltage is applied to a liquid crystal. Here, the overshoot amount, if a gray-level value in a current frame is larger than a gray-level value in one past frame, becomes large, as shown as Vb (tb≦t≦tc) in FIG. 16, so that a specified overvoltage being higher than a voltage corresponding to a gray-level value in a current frame is applied to a liquid crystal layer and, if a gray-level value in a current frame is smaller than a gray-level value in one past frame, becomes small, as shown as Vd (tf≦t≦tg) so that a specified voltage being lower than a voltage corresponding to a gray-level value in a current frame is applied to a liquid crystal layer. Thus, a movement of a liquid crystal is speeded up to reach a target gray level so that a liquid crystal layer corresponding to the target gray level has specified transmittance before the completion of the liquid crystal response.
For example, as shown in FIG. 15, when transmittance T is to be changed from Ta (ta≦t≦tb) to Tb (tb≦t≦tc, tc≦t≦td, td≦t≦te, te≦t≦tf), though an original applied voltage (target voltage) V corresponding to the voltage Tb is, as shown in FIG. 16, Vc, by applying an overvoltage Vb exceeding the voltage Vc, at time (tb≦t≦tc), to rapidly raise the voltage V from Va, jumping over Vc and to Vb, a response speed of a liquid crystal display panel can be made higher. Similarly, when transmittance T is to be changed from Tb (tb≦t≦tc, tc≦t≦td, td≦t≦te, te≦t≦tf) to Tc (tf≦t≦tg, tg≦t≦th, th≦t≦ti), though an original applied voltage (target voltage) V corresponding to the voltage Tc is, as shown in FIG. 16, the voltage Ve, a voltage Vd being lower than the voltage Ve is applied at time (tf≦t≦tg).
However, as shown in FIG. 15, in some cases, an excessive response in which transmittance T exceeds transmittance Tb corresponding to a target gray level occurs (reached gray level is larger than a target gray level) in a frame (tc≦t≦td) subsequent to a frame (tb≦t≦tc) in which an overshooting driving operation is performed, which causes degradation of displaying quality. Therefore, an amount of overshooting driving was not sufficient conventionally. That is, there was no choice but to suppress an overshoot amount in necessary frames to prevent an excessive response in a succeeding frame.
To solve this problem, technology is disclosed (for example, Patent Reference 2 [(Japanese Patent Application Laid-open No. 2004-1093329)] in which a pattern of transition in gray levels from a gray level existed at least two frames before up to a gray-level in a current frame is detected and, when the gray-level transition pattern is a predetermined one, the driving is performed so that an overshoot amount is decreased. The disclosed liquid crystal display device 201, as shown in FIG. 17, has a liquid crystal display panel 202 and a driving circuit 203 to drive the liquid crystal display panel 202. The driving circuit 203, as shown in FIG. 17, includes an overshoot calculating section 204 to calculate a proper overshoot amount, a storing section 205 to store processing programs, various blocks of data, or a like, a timing control section 206 to control output timing of video signals, a data electrode driving circuit 207 to supply display signals (data signals) to each signal line of the liquid crystal display panel 202, and a scanning electrode driving circuit 208 to supply scanning signals to each scanning line.
The storing section 205 has frame memories 209 and 210 and an LUT storing section 211 to store many LUTs. Each of the frame memories 209 and 210 stores image data [(n−1)-th frame video data: Fn−1] existed one frame period before relative to image data (n-th frame video data: Fn) to be displayed in one frame this time and image data [(n−1)-th frame video data: Fn−1] existed two frame periods before relative to image data (n-th frame video data: Fn) to be displayed this time in one frame. Moreover, the LUT storing section 211 stores a lot of LUTs including gray level data for overshooting driving corresponding to transition in gray levels. In each of the LUTs, an overshoot amount corresponding to transition of gray levels (combination of a gray level in one past frame and a gray level in a current frame for displaying) is shown. The overshoot amount varies for each LUT and a corresponding LUT is selected responsive to a pattern of transition in detected gray levels.
The first problem to be solved is that, even when the conventional technology disclosed in the Patent Reference 1 is applied in which a measure is taken by decreasing the overshoot amount under a specified condition, a sufficient overshooting driving can not be performed and it is made impossible to reliably improve a response speed to provide excellent quality of display. Also, the second problem to be solved is that, even when, for example, the conventional technology disclosed in the Patent Reference 2 is applied, an increase in capacity of a frame memory occurs and many LUTs become necessary and an amount of calculation for judging processes or a like is increased, as a result, causing a rise in costs. For example, the capacity of frame memory to store at least two frames of image data are required as a result.